In his first major foreign policy speech as candidate, Rubio laid out a vision of a robust United States that would protect threats to global commerce from China and Iran and stand up to Russian President Vladimir Putin and Islamic State.

He said Clinton, the front-runner to be the Democratic presidential candidate in 2016, had made major mistakes like trying to reset relations with Moscow during her four years as America's top diplomat.

"We simply cannot afford to elect as our next president one of the leading agents of this administration's foreign policy, a leader from yesterday whose tenure of secretary of state was ineffective at best and dangerously negligent at worst," he told the Council on Foreign Relations in New York.

The U.S. senator from Florida outlined a tough approach to world affairs at a time when China is attempting to assert greater control over the South China Sea, a vital shipping route, and Iran has threatened commercial shipping in the Strait of Hormuz.

A member of the Senate Foreign Affairs and Intelligence Committees, Rubio has made international affairs a main focus of his bid to win the Republican nomination for the White House in 2016.

He receives foreign affairs advice from aides who were linked to the last Republican president, George W. Bush.

But Rubio appeared to back-track from previous support for the 2003 invasion of Iraq, when asked whether he would have supported it based on what is known now.

"Not only would I not have been in favor of it, but President Bush wouldn't have been in favor of it."

Rubio, a son of Cuban immigrants, in March said the invasion was not a mistake and the world is better off without Saddam Hussein.

Earlier this week, the Iraq issue caused a headache for Jeb Bush, a potential rival of Rubio for the Republican nomination, after saying he would have authorized the U.S. invasion given the intelligence available at the time.

CLINTON AND TRADE

Rubio is in sixth place in a Reuters/Ipsos online poll of Republican hopefuls and potential candidates for the November 2016 presidential election, although it is early in the race and no person in the survey gets more than 15 percent of the vote.

Rubio mentioned Hillary Clinton by name, accusing her of not taking a strong enough pro-trade position in the fight over a Pacific Rim trade treaty that pits Senate Democrats against President Barack Obama.

"Those such as Secretary Clinton, who preach a message of international engagement and 'smart power' yet are not willing to stand up to special interests and support free trade are either hypocritical or they fail to grasp trade's role,” Rubio said.

In a reference to China and Iran, Rubio said he would challenge nations that disrupted trade in "choke points such as the South China Sea or the Strait of Hormuz."